| Summary: | The kinetics and mechanism of the place exchange reaction(PER) of alkylthiols with alkylthiol-protected gold nanoparticles(AuNP) are investigated. Using chemically similar alkylthiols it was possible to study the reaction in the absence of perturbing factors, enabling detailed mechanistic and kinetic studies to be explored. It is found that the reactions are zero order in incoming ligand and overall follow a second order diffusion limited Langmuir rate law. In the case where there is little chemical distinction between the incoming and capping ligands, the reactions proceed to an endpoint consistent with a Keq=1. The rate of the reaction is dependent on the chain length of the capping ligand and the AuNP core size. The related dialkyldisulphide for-alkylthiol AuNP exchange reaction is consistent with the same rate law and also proceeds to a well-defined endpoint. However, the rate constant is 20-fold less than the alkylthiol case. These results lead to a convergent model of PERs where the rate limiting process involves both incoming and outgoing ligands, with diffusion of the incoming ligand to the AuNP surface as the major controlling factor of the reaction rate.
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